A conventional apparatus is described in German Patent No. 28 23 067. In this German Patent, the coasting air recirculation valve is activated exclusively pneumatically by the intake duct pressure: the coasting air recirculation valve opens when a certain negative pressure, occurring while the vehicle is in coasting mode, is present in the intake duct on the outflow side of the throttle valve. The fact that the outlet of the compressor is connected to its inlet via the coasting air recirculation line causes a decrease in the boost pressure in the intake duct downstream from the compressor, which is expressed as better engine response to rapid closing of the throttle valve. The opening or closing behavior of the coasting air recirculation valve is not optimally defined in the case of activation exclusively by way of the intake duct pressure.
U.S. Pat. No. 5,083,543 describes a coasting air recirculation valve which has its control pressure delivered from a negative pressure vessel. This negative pressure vessel is fed from the intake duct pressure. The coasting air recirculation valve is thus controlled solely as a function of the intake duct pressure.
Japanese Patent Application No. 06 117 263 (provided in, e.g., Patent Abstracts of Japan, Vol. No. 408, Jul. 29, 1994) describes a coasting air recirculation valve which is controlled as a function of the negative pressure in the intake duct on the downstream side of the throttle valve, and which is located in a coasting air recirculation line. Inserted in a line between the intake duct downstream side and the coasting air recirculation valve is a vacuum vessel whose negative pressure depends solely on the negative pressure in the intake duct on the downstream side of the throttle valve. The purpose of the vacuum vessel is to damp air flow noises that occur when the coasting air recirculation valve is opened.
It is therefore the object of the present invention to describe an apparatus of the kind cited initially that allows highly defined opening and closing of the coasting air recirculation valve.